Not applicable.
The present invention relates to fuel delivery systems for stationary and propulsion gas turbine engines, and in particular, to rocket and jet engine fuel delivery systems having fuel metering pumps.
The high burn rates of rocket and jet engines requires the fuel delivery system to be capable of precisely metering fuel. Traditionally, fuel delivery systems for rocket and jet engines, particularly those used for propulsion, have included a fuel pump, a pressure accumulator and a fuel metering device, all of which being separate components mounted on or near the engine at distinct locations and coupled to the engine and fuel source by suitable fuel lines. The accumulator operates to dampen pulsation or ripple in the fuel caused by the pump so that the metering device can accurately dispense the appropriate amount of fuel to the engine fuel atomizer. The use of multiple components is expensive and occupies space, which is limited for propulsion systems.
It is desirable to reduce the number of components in the fuel delivery by combining the fuel pump and metering device into one unit. However, if one component is to serve as both the pump and the metering device, it must meet the requires of the rocket and jet engine industry for both the pump and the metering device. Some of the attributes of a jet engine fuel pump include the ability to pump particle contaminated fuel for an extended time period. It must have good dry lift capacity and be able to operate with vapor-to-liquid ratios at the pump inlet of 0.45 or greater. Moreover, if no accumulator or fluid muffler is to be used, the pump must also be able to provide generally non-pulsating fuel flow. The requirements of a jet engine metering device include low power consumption and low hysteresis, i.e., the ability to operate with high efficiency and low friction. The device must also be able to provide a wide range of flow rates accurately, i.e., have a high turn-down ratio. Additionally, the device must be compact and have minimal internal leakage.
Typically in the rocket and jet industry, the fuel delivery systems employ gear pumps which create a pressure differential by moving the fuel through a series of intermeshing teeth running at a high frequency. Gear pumps consume a lot of power and leak internally and are therefore less than ideal for rocket and jet engine use. Moreover, due to reliability concerns, gear pumps used for propulsion applications typically are powered by an engine driven gear box (rather than an electric motor) and therefore must be coupled to a separate metering valve via suitable fuel lines, which increases expense and occupies additional space.
The inventor of the present invention has recognized that a compact and reliable fuel delivery system meeting the stringent requirements of rocket and jet engine applications could be achieved using a specially designed constant pressure, cam operated metering pump with rolling diaphragms that prevent degradation of the pump from fuel and contaminants.
Specifically, the present invention provides a system for supplying combustible fuel to a fuel consuming device. The deliver system includes a fuel metering pump pumping combustible fuel from a fuel source through a fuel line to the fuel consuming device. The fuel metering pump has a housing defining an outlet port and an inlet port. The inlet port is in communication with the fuel source and a pair of pump chambers. Each pump chamber is sealed by a diaphragm to which is connected a pumping member biased at one end to abut a motor driven face cam. The face cam is operated by the motor to alternately reciprocate the pumping members through pump and suction strokes within the pump chambers. The fuel metering pump meters substantially constant pressure fuel through the fuel line to the fuel consuming device without the need for an accumulator or separate metering valve.
In a preferred form, the fuel consuming device is a gas turbine, rocket or jet engine. The gas turbine engine may be for a stationary or land-based vehicular applications or for propulsion of air and space vehicles. The fuel delivery system, however, is also particularly suited for use with fuel cells.
In another preferred form, the fuel source includes a fuel tank and the pump housing is mounted to the fuel tank over an opening therein. In this way, no input fuel lines are required and the vapor-to-liquid ration of the pump is maximized.
In yet another preferred form, the fuel delivery system of the present invention further include an electronic controller for controlling the speed of an electric motor driving the face cam. A speed sensor is electrically coupled to the controller and positioned near the circumference of the face cam. The face cam has teeth at its circumference that are detected by the sensor and used by the controller to operate the motor.
One aspect of the invention is that the face cam includes an increasingly ramped cam surface extending through more than 180 degrees, which abuts cam followers to move the pumping members through the pump and suction strokes. Preferably, the raised ramped surface extends to 200 degrees providing a 20 degree overlap wherein both pumping members are in the pump stroke. This provides a smooth transition from the pumping stroke to the suction stroke of each pumping member. In this way, the face cam imparts a constant velocity motion to the pumping members so as to minimize pressure ripple associated with swash plates of traditional piston pumps. This non-pulsating fuel flow makes the pump particularly well suited for use in high precision applications such rockets and jet engines.
Another aspect of the invention is that the ambient side of the pump chambers is sealed from the fuel by the diaphragms, which prevent fuel, contaminants and debris from entering the cam chamber and the electric motor. This also obviates the need for expensive close fitting surfaces in the pump chambers with highly polished surfaces. As such, little or no internal friction occurs, which maximizes efficiency and resistence to contaminated fuel. The seal of the diaphragms ambient air in the pump chambers to vent to the cam chamber of the housing. The pumping action then causes equal cross-transfer of displaced air volume, thereby eliminating pressure build up in the pump chambers. Moreover, the seal of the diaphragm eliminates the need for an external motor shaft seal.
The present invention also provides a fuel metering pump suitable for delivering fuel to rockets and jet engines. Specifically, the pump includes a drive mechanism comprising a drive motor having an axial shaft and a disk-shaped face cam mounted to the motor shaft having a ramped cam surface at an outer face. The ramped cam surface of the face cam extends radially more than 180 degrees so that both pump mechanisms are simultaneously in the pump stroke for a portion of the pump stroke and so that the pumping members alternately reciprocate through the suction and pump strokes at essentially a constant velocity. The pump also includes a pair of pumping members movable through opposite suction and pump strokes and disposed in separate pump chambers defined by a housing mounted over an orifice of a fuel tank. The housing has an inlet controlled by a reed valve to be in communication with the fuel. Each pumping member includes a cam roller biased against the face cam by a spring so as to be contacted by the ramped cam surface. A connector rod is connected to the cam roller at one end and a head plate is connected at the opposite end of the connector rod. A fuel resistant diaphragm is attached to the head plate so as to roll back as the pumping members are moved through the suction and pump strokes.
These and still other advantages of the present invention will be apparent from the description of the preferred embodiments which follow.